Complex compounds which contain, as the central atom, a metal of group VIII of the Periodic Table of the Elements (IUPAC Version) and, as ligands, P(III) compounds, i.e. phosphines or phosphites and, if appropriate, further groups which are capable of forming complexes, have found increasing use in recent years as catalysts for organochemical syntheses. Thus, the reaction of olefins with synthesis gas to give aldehydes (hydroformylation), which is practiced widely on an industrial scale, is carried out in the presence of catalyst systems which comprise cobalt--and, in particular, rhodium--and triphenylphosphine. Catalysts based on complex compounds containing phosphine have also proven suitable for the reaction of methanol with synthesis gas to give higher alcohols, in particular ethanol and propanol (homologation). In the cases mentioned, the ligands are usually present in excess, so that the catalyst system comprises the complex compound and free ligand. The reactions take place in a homogeneous phase, according to the solubility of the catalysts in organic media.
The reaction can also be carried out in a heterogeneous reaction system. An advantage of this process variant is the easy and gentle separation of the catalyst dissolved in water from the water-insoluble reaction product. The process described in DE-C2 27 00 904 for the preparation of nitriles by addition of hydrogen cyanide to unsaturated organic compounds containing at least one ethylenic double bond operates, for example, in accordance with this principle. For the preparation of aldehydes by reaction of olefins with carbon monoxide and hydrogen, rhodium is employed as metal or in the form of its compounds together with a water-soluble phosphine, for example the alkali metal salt of tri(m-sulfonatophenyl)phosphine, ("TPPTS") as the catalyst according to the process of DE-C2 26 27 354. Further examples of reactions with a heterogeneous catalyst phase are to be found in Angew. Chem. 1993., 105, 1588 et seq.
Although the foregoing two-phase processes have proven to be particularly appropriate on the industrial scale, recent work has perfected them further. An attempt has been made to increase the activity of the catalysts by modification of the complexing ligands and to prolong their activity, in order to reduce the specific catalyst requirements--both for the metal and for the ligand--and therefore the production costs. Economic grounds are also a decisive reason for working towards a significant reduction in the phosphine/metal ratio. Finally, attempts are being made to develop ligand systems which solve individual--e.g. product-specific-problems in the context of known processes. Furthermore, novel fields of use are being sought for these diverse catalyst systems.